Observational Appearances of Magnetically Charged Black Holes in Born-Infeld Electrodynamics

TL;DR

This study explores how magnetically charged black holes in Born-Infeld electrodynamics appear observationally, focusing on shadows, photon spheres, and accretion effects, revealing the dominance of direct emission in shadow width.

Contribution

It provides the first detailed analysis of black hole shadows in Born-Infeld electrodynamics considering magnetic charge and accretion effects, using backward ray tracing and transfer functions.

Findings

Black hole shadows are darker with infalling accretion.

Photon sphere radius is independent of accretion type.

Shadow width is mainly influenced by direct emission.

Abstract

In this paper, we investigate the observational appearances of magnetically charged black holes in Born-Infeld (BI) electrodynamics. We examine the effects of the magnetic charge and the BI parameter on the geodesics with different impact parameters. Using the backward ray tracing method, we investigate how spherically symmetric accretions interact with black hole shadows and photon spheres. The shadows of infalling accretion are darker than that of static ones. And the radius of the photon sphere is an intrinsic property of the spacetime that is independent of accretions. We then study how the thin disk models affect the black hole shadows. After obtaining the transfer functions, we divide photons emitted from the thin disk into three categories: direct emission, lens ring, and photon ring. Applying three emission models, we find that the width of the shadow is dominated by the direct emission, the photon ring and the lens ring can hardly be identified by changing the emission models.